The invention resides in a flywheel for mounting to an internal combustion engine and coupling to a machine driven thereby, including a flywheel flange and coupling means for coupling the machine to the flywheel. The invention also relates to an internal combustion engine including a flywheel and a system comprising the internal combustion engine and the machine to be driven as well as the use of such a system.
Internal combustion engines are usually connected electrically to a reference potential, for example to ground, via a ground cable connected to the crankcase of the engine. With the use of an internal combustion engine in connection with a system including a machine to be driven thereby such as a generator for example, in a motor-generator unit, the generator is coupled to the engine for example via a clutch disc. A clutch disc may specifically be mounted for rotation with the crankshaft of the internal combustion engine and may be coupled in a suitable way to the shaft of a generator.
Because of an electromagnetic induction generated in the shaft of an electric machine to be driven, with the electrically conductive coupling means generally used so-called shaft voltages can be generated in the crankshaft which are also effective at the bearings of the crankshaft. This may cause problems because the bearings may be damaged by electro-erosion. A reason herefor may be electric discharges through the thin lubricant films present in the bearings as a result of the voltages present in the shaft. The discharges may result in material ablation or material displacement at the bearing surfaces. In the worst case, the crankshaft bearings or other parts of the internal combustion engine may be severely damaged.
DE 10 2004 025 665 134 assigned to the assignee of the present application describes a solution for avoiding shaft voltages and the formation of creeping currents between the crankshaft, a housing and the reference potential. The solution resides in providing a low-resistance path for the creeping currents. To this end, DE 10 2004 025 665 B4 provides a current collector including a rotor which is connected for rotation with a rotor connected to the crankshaft and a stator connected the crankcase of the internal combustion engine wherein the stator includes an electrically well conducting structure between the rotor and a reference potential in the stator. The conducting structure includes for example carbon brushes. Basically, such a structure is subject to wear and requires servicing because of the dynamic contact between the rotor and the stator.
An alternative solution is disclosed in Applicants DE 10 2004 037 178 A1. In this case, for an internal combustion engine a flywheel is used which comprises a single piece and forms part of a clutch wheel which includes a clutch disc that is flanged to the flywheel. The clutch disc of the clutch wheel serves to connect the machine to be driven by the internal combustion engine, for example an electric generator, to the engine. Here, the flange and/or clutch disc consist of an electrically non-conductive material so that the crankshaft of the internal combustion engine is electrically insulated from the machine to be driven. This basically good solution however has been found to be comparably expensive in certain applications or at least in need for improvement.
Actually, a solution would be desirable wherein shaft voltages in an internal combustion engine could be avoided by a simple flywheel design which is electrically insulating.
It is therefore the object of the present invention to provide an arrangement and a use, by which electric voltages in shafts of internal combustion engines can be avoided in a relatively simple manner in particular by means of an electrically insulating flywheel for coupling the internal combustion engine and the electrical machine to be driven thereby, which flywheel is of comparatively simple design and can be manufactured at relatively low costs.